1. Field of the Invention
The present invention relates to an apparatus for combining rotations of outer and inner coaxial shafts driven by independent external power drives and permitting the inner shaft to rotate at a contorolled speed. A relative rotation transmitting apparatus according to the present invention may be applied to a boring machine. Then, a boring tool is fixed to the ends of the outer and inner shafts, thereby permitting the tool to rotate and radially move relative to a workpiece.
2. Description of the Prior Art
A conventional boring machine uses a differential gear to transmit driving power from an exterior power drive and rotate an inner shaft within a rotating coaxial outer shaft.
Such power transmission using a differential gear is, in fact, difficult in design because many designing factors must be satisfied.
Differential gears are complicated in structure, and are expensive. They are not appropriate to the precision feeding of a member while rotating at a high speed. Only a large-sized boring machine can use a differential gear in its power transmission.
A small-sized boring machine uses cam-and-link mechanisms in place of a differential gear. Specifically, an elongated rod is inserted in a hollow rotating shaft, and cam-and-link mechanisms are connected both to the elongated rod and the rotating shaft to convert the rotation of the shaft to the linear feeding motion of the elongated rod. The linear feeding motion, however, is limited to a relatively short stroke. Also, disadvantageously the elongated rod is flexible, and it will yieldingly bend when pushed against a stationary workpiece. Therefore it cannot feed a boring tool with high precision.